Method, computer program, and control and/or regulating appliance for operating an internal combustion engine, and internal combustion engine

ABSTRACT

In an internal combustion engine, fuel is injected directly into a combustion chamber by an injector that has a piezoactuator. An electrical charge conveyed to and/or removed from the piezoactuator is ascertained by a method that is calibrated at least once during an operating time span of the internal combustion engine. To allow the calibration to be carried out or performed as often as possible, the method for ascertaining the electrical charge transferred to and/or removed from the piezoactuator may be calibrated during at least one triggering off-time (dtK) of the piezoactuator while the internal combustion engine is operating.

FIELD OF THE INVENTION

The present invention relates firstly to a method for operating aninternal combustion engine in which fuel is injected directly into acombustion chamber by an injector that has a piezoactuator, and in whichan electrical charge conveyed to and/or removed from the piezoactuatoris ascertained by way of a method that is calibrated at least onceduring an operating time span of the internal combustion engine.

BACKGROUND INFORMATION

European patent document no. 1 138 915 refers to a method in which,during charging of a piezoactuator of an injector, the transferredquantity of electrical charge can be determined. The correspondingquantity of electrical charge transferred during discharging of thepiezoactuator can likewise be determined. This is accomplished byintegration of a current signal. In order to reduce errors uponintegration of the current signal and thereby to increase the precisionwith which the transferred charge quantity is ascertained, an alignmentof the integration process, to be performed at specific points in time,is proposed. This alignment is to be performed, in particular, when theinternal combustion engine is started. The reason for this is thatordinary control unit concepts and output stage concepts can operateonly sequentially, so that an alignment cannot occur during triggeringof the output stage or the piezoactuator.

SUMMARY OF THE INVENTION

An object of an exemplary method of the present invention is to providethat the electrical charge conveyed to and removed from thepiezoactuator can be determined with even higher precision.

This object may be achieved, in the context of the method, in that themethod for ascertaining the electrical charge conveyed to and/or removedfrom the piezoactuator is calibrated during at least one triggeringoff-time of the piezoactuator during operation of the internalcombustion engine.

With the exemplary method according to the present invention, theelectrical charge transferred to and removed from the piezoactuator thatis ascertained can be aligned not only before the internal combustionengine is started, but also during normal operation thereof. Triggeringoff-times of the piezoactuator, which occur even during normal operationof the internal combustion engine, are used for this purpose.

This is because, in contrast e.g. to magnetic actuators, a triggering ofthe piezoactuator takes place or occurs only during the actual change inlength of the piezoactuator. For a change in length of this kind, aspecific electrical charge is transferred to, or a specific electricalcharge is removed from, the piezoactuator. Between these triggeringactions are triggering off-times in which the piezoactuator, and theoutput stage that generally triggers it, are “idle.”

With the present alignment and triggering method, even though theindividual actions are executed sequentially, an alignment of the methodwith which the charge transferred to and removed from the piezoactuatoris ascertained can be performed while the internal combustion engine isoperating normally.

Since alignment can be performed even during operation of the internalcombustion engine, drift phenomena resulting, for example, from changesin the temperature of a control unit can be compensated for even duringoperation of the internal combustion engine. The precision with whichthe method for ascertaining the electrical charge delivered to andremoved from the piezoactuator is performed may thus be greatlyimproved.

As a result of the more precise determination, according to theexemplary embodiment of the present invention, of the actuatorcapacitance, the actuator temperature can be more accuratelyascertained. This may have a direct effect, however, on the linearstroke characteristics of the piezoactuator, and thus on the accuracy ofthe opening and closing behavior of an injector equipped with thepiezoactuator. An accurate knowledge of actuator capacitance thus,ultimately, also allows the internal combustion engine to be operatedmore optimally in terms of emissions and consumption.

It is understood that the exemplary method according to the presentinvention can be used in the same fashion in both gasoline and dieselinternal combustion engines. The use of, for example, an exhaust gasturbocharger and/or an exhaust gas recirculation system also does notconflict with utilization of the exemplary method according to thepresent invention.

In another exemplary embodiment, the calibration be accomplished withthe injector open, in the triggering off-time between the end of anopening triggering action and the beginning of a closing triggeringaction. An open injector is present at each injection of fuel into thecombustion chamber. Thus, the calibration may be performed at almostevery working cycle of a cylinder of the internal combustion chamber(except during overrun of the engine, in which the injector remainsclosed). Such frequent calibration allows for reaction even toshort-term fluctuations in the temperature of the control unit, thusconsiderably improving the accuracy of the method with which the chargeconveyed to and removed from the piezoactuator is determined.

Calibration with the injector open may also have the advantage that thecalculations required for this purpose can be performed relativelyeasily shortly before the injection. If it were desired instead to usethe unoccupied phases between two injections for calibration, this wouldrequire laborious calculation because the end of one injection is knownonly shortly before the actual injection, and moreover the beginning ofthe subsequent injection would already have to be known. This may notusually be the case.

In addition, lead corrections may be necessary because of the dynamicsof the internal combustion engine, since the respective beginning of aninjection is referred to the crankshaft, whereas the duration of aninjection has a time reference. This entire problem may be circumventedif the calibration is performed with the injector open.

Also, for each working cycle of a cylinder of the internal combustionengine, at least one secondary injection and one main injection may beprovided, and the calibration be performed during a main injection. Thisinjection type occurs more often than all other injection types, sincethe torque of the internal combustion engine is created principally bythe main injection, and the main injection is therefore normally alwaysperformed (except during overrun or the like). In addition, the durationof the main injection is relatively long as compared with the otherinjection type (preinjection, postinjection, etc.), so that acomparatively long time is available for calibration.

Advantageously, a check may be made before a calibration, in arotation-speed-synchronous dynamic interrupt, as to whether the timebetween two triggering actions is sufficient for a calibration. Thereason for this is that the triggering duration may be calculated in adynamic interrupt of this kind immediately before the injection. Thetriggering duration is defined here as the time span between thebeginning of charging of the piezoactuator and the beginning ofdischarging of the piezoactuator. Subtracting the maximum possiblecharging time from the beginning of charging, i.e. from triggeringinitiation, yields the time remaining for a calibration. Performing thecheck in the rotation-speed, synchronous interrupt, as with theexemplary embodiment of the present invention, which may allow thischeck to be performed at the latest possible point in time, andtherefore with greater accuracy.

The dynamic interrupt is thus also the ideal time at which to programthe calibration itself. This is expressed in the exemplary methodaccording to the present invention in which an instruction necessary forthe calibration is determined in a rotation-speed-synchronous dynamicinterrupt.

The calibration itself may be particularly accurate if it encompasses aplurality of individual calibration actions. To identify whether thetriggering duration of the piezoactuator calculated in the dynamicinterrupt is sufficient for one or more calibration actions, thefollowing procedure may be used:modulo (number of calibration actions)=triggering time/maximum time fora calibration instruction plus maximum charging time.

In another exemplary method of the present invention, the number ofactions possible per working cycle of a cylinder is limited to aspecific value, and only as many calibration actions as will permit allthe intended injection actions to be performed are allowed during oneworking cycle of a cylinder. In this manner, therefore, a maximumpossible number of actions may be ascertained a priori as a function ofthe absolute length of a working cycle, the injection actions having ahigher priority than the calibration actions.

This can be implemented since an action coordinator firstly identifiesthe number of injection actions that have been ordered, and thendetermines the number of calibrations still possible. This may ensurethat operation of the internal combustion engine is not impaired by thecalibration actions. At the same time, however, there is an assurancethat a calibration can be performed as soon as the “time window”required for it is open.

To a certain extent, the advantages according to the exemplary method ofthe present invention may already be achieved if a calibration action isscheduled not regularly at frequent intervals, but instead at least whenthe temperature of a control unit has changed by at least a specificvalue since the last calibration action. This reduces the computationload on the control unit and takes into account the fact that thetemperature profile of the control unit has a considerable influence onthe accuracy with which the electrical charge conveyed to and removedfrom the piezoactuator is determined.

In addition or alternatively thereto, a calibration action may bescheduled at least after expiration of a specific time interval, theduration of the time interval increasing in a defined manner after astartup of the internal combustion engine. This takes into considerationthe fact that the temperature of the control unit changes relativelysignificantly after the internal combustion engine is started, whereasafter a certain time it remains more or less steady. Calibrations arenecessary only relatively seldom during this quasi-steady phase, whichrelieves stress on the control unit.

As an alternative to the aforesaid calibration operation with theinjector open, the calibration can also be performed during an overruncondition of the internal combustion engine. During this overrun theinjector is closed, i.e. is not being triggered, so that a relativelylong period of time is available for calibration.

Given a certain driving style or corresponding traffic conditions,however, an overrun condition of the internal combustion engine maypossibly occur only seldom or not at all. In addition, a number oftests, alignment or learning processes (e.g. injection quantitycalibration), and a catalytic converter regeneration are performedduring the internal combustion engine's overrun shutdown, makingpotential calibration difficult or impossible.

The exemplary embodiment and/or exemplary method of the presentinvention also concerns a computer program that is suitable for carryingout or performing the above method when it is executed on a computer.The computer program may be stored in a memory, in particular in a flashmemory.

The exemplary embodiment of the present invention further relates to anopen- and/or closed-loop control unit for operating an internalcombustion engine, which unit encompasses a memory on which a computerprogram of the aforementioned kind is stored.

Also the subject matter of the exemplary embodiment and/or exemplarymethod of the present invention is an internal combustion engine havingat least one combustion chamber, at least one injector that injects fueldirectly into the combustion chamber, and at least one piezoactuator. Insuch an internal combustion engine, it may be advantageous if itencompasses an open- and/or closed-loop control unit of theaforementioned kind.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an internal combustion engine with directfuel injection, encompassing an injector having a piezoactuator.

FIG. 2 is a diagram depicting the charge state of the piezoactuator ofFIG. 1 as a function of crank angle.

FIG. 3 is a diagram indicating how many injection actions are to beperformed for a given pressure in a fuel system and a given rotationspeed of a crankshaft of the internal combustion engine.

FIG. 4 is an enlarged portion of the diagram of FIG. 2.

FIG. 5 is an execution diagram which is used to determine whether toschedule a calibration of a method with which the electrical chargeconveyed to and removed from the piezoactuator of FIG. 1 is ascertained.

FIG. 6 is a block diagram of a method for coordinating various actionsduring operation of the internal combustion engine of FIG. 1.

DETAILED DESCRIPTION

In FIG. 1, an internal combustion engine bears the overall referencecharacter 10. It has several cylinders. of which only the one having thereference character 12 is depicted in FIG. 1. It encompasses acombustion chamber 14 to which combustion air is conveyed through anintake valve 16 and via an intake duct 18. A throttle valve 20 controlsthe quantity of intake air conveyed, which in turn is sensed by an HFMsensor 22.

An exhaust valve 24 directs the exhaust gases into an exhaust duct 26,where they are purified by a catalytic converter 28 that has a lambdaprobe 30. Fuel is conveyed to the combustion chamber 14 by an injector32 whose valve element (not depicted) is actuated by a piezoactuator 33.Fuel is made available to injector 32 at very high pressure from a fuelsystem 34. An ignition system 36 triggers a spark plug 38.

The rotation speed of a crankshaft 40 is picked off by a rotation speedsensor 42 which supplies a corresponding signal to an open- andclosed-loop control unit 44. HFM sensor 22 and lambda probes 30 alsosupply signals to open- and closed-loop control unit 44. Open- andclosed-loop control unit 44 triggers piezoactuator 33, ignition system36, and throttle valve 20, inter alia.

It is known that the linear stroke characteristics of piezoactuator 33depend on its temperature. The accuracy of the opening and closingbehavior of injector 32 thus also depends on the temperature ofpiezoactuator 33. This in turn has an impact on the emissions andconsumption behavior of internal combustion engine 10. An accurateknowledge of the temperature of piezoactuator 33 is thereforeadvantageous. One possibility for determining the temperature ofpiezoactuator 33 is based on knowledge of the capacitance ofpiezoactuator 33. That in turn can be ascertained by determining theelectrical charge conveyed to and removed from piezoactuator 33.

These charge quantities are usually determined by integrating a currentsignal. The result of this integration also depends, however, onsecondary factors. These include, for example, the temperaturedependency of the properties of the electrical circuits of open- andclosed-loop control unit 44. To allow the integration to be performedwith high accuracy, an alignment or calibration is therefore necessaryfrom time to time.

Since the processor used in open- and closed-loop control unit 44 canusually operate only sequentially, however, a time window in which it iscertain that the processor is not occupied with other actions must befound for this alignment. As discussed in detail below, it is proposedin the present exemplified embodiment to use as the time window atriggering off-time that is present when injector 32 is open.Consideration is given, in this context, to the fact that thecalibration encompasses a plurality of individual calibration actions,in the present case a total of three.

FIG. 2 depicts the present voltage U of piezoactuator 33 during oneworking cycle of cylinder 12. A change in voltage U causes a change inthe length of piezoactuator 33 and thus an opening or closing motion ofthe valve element of injector 32. As is evident from FIG. 2, in theinstance considered here fuel is introduced from injector 32 intocombustion chamber 14 by way of a total of three individual injections.In order to open injector 32 for an injection, piezoactuator 33 mustmodify its length. For an opening of injector 32, the charge state ofpiezoactuator 33 is changed, for that purpose, from a potential U1 to apotential U2. In the reverse order, the potential is modified in orderto close injector 32 and terminate the injection.

In FIG. 2 a first preinjection bears the reference character 46, a maininjection the reference character 50, and a first postinjection thereference character 52. The number of possible injections depends on avariety of factors, including the fuel pressure p in fuel system 34 andthe rotation speed n of crankshaft 40 (see FIG. 3). Because of theenergy balance of control unit 44 and the volume balance of thehigh-pressure fuel pump (not depicted in FIG. 1), fewer injections takeplace at high rotation speeds (field 56 in FIG. 3) than at low rotationspeeds and low fuel pressure (field 58 in FIG. 3).

The change over time in voltage U of piezoactuator 33 for main injection50 is depicted in enlarged form in FIG. 4. It is evident from this thatthe data governing the duration of main injection 50 are determined at acrank angle W0 in a dynamic interrupt that bears the reference character60 in FIGS. 2 and 4. Those data include the beginning of the dischargingoperation of piezoactuator 33, which in the present case is located at acrank angle W1. The beginning of the charging operation of piezoactuator33 is ascertained in a static interrupt that is located earlier in timethan the dynamic interrupt, and is not indicated in the Figure.

The beginning of the discharging operation of piezoactuator 33 isdetermined from a triggering duration dtA that is ascertained in dynamicinterrupt 60 at crank angle W0. This is the time between the beginningof charging operation 62 and the beginning of a discharging operation 64of piezoactuator 33. Subtracting the maximum possible charging time dtLof piezoactuator 33 from triggering duration dtA yields a time span dkKthat is available for other actions.

The basis for all this is the fact that the processor used in open- andclosed-loop control unit 44 can operate only sequentially. In thepresent case, the remaining “free” time dtK between the two triggeringactions 62 and 64 of piezoactuator 33 is sufficient for three adjustmentor calibration actions 66, 68, and 70. The fact that the processor ofopen- and closed-loop control unit 44 can carry out these threecalibration actions 66, 68, and 70 was ascertained previously by anaction coordinator whose operation will now be explained with referenceto FIG. 5.

Reference character 72 in FIG. 5 refers to the enabling of the optimumnumber of injections for the present operating state (driver's requestedtorque, rotation speed, etc.). In 74, these injections are each given anindividual priority. In block 75, the maximum number of injectionspermissible under the existing operating conditions is defined. This isaccomplished by way of a minimum selection that depends, inter alia, onthe charge state of an output stage (block 76) and on the deliveryvolume and delivery pressure of fuel system 34 (block 78).

If the maximum permissible number of injections defined in 75 is lessthan the number of injections enabled in 72 itself, a selection is madein block 80 of those injections which have the highest priority andwhose quantity corresponds to the number ascertained in 75. Only thoseinjections are carried out. In the present exemplified embodiment atotal of three injections, i.e. preinjection 46, main injection 50, andpostinjection 52, are permitted to be carried out.

In 81, the maximum number of actions that can be processed by open- andclosed-loop control unit 44 between two static interrupts of the sametype is made available (a separate static interrupt being allocated onthe one hand to the preinjection and on the other hand to the maininjection and postinjection, so that the number of static interruptswithin two crankshaft revolutions is equal to the number of cylinders ofthe internal combustion engine multiplied by a factor of two). In thepresent exemplified embodiment it is six.

A subtraction in 82 then defines the number of actions still possiblefor calibration, which in the present case is three, corresponding tocalibration actions 66, 68, and 70 of FIG. 4. This ensures that theinjection actions take priority over the adjustment or calibrationactions, but that the maximum number of calibration actions in the givencircumstances can nevertheless be performed.

FIG. 6 depicts a method which determines those instances in which anycalibration actions at all are to be performed. The basis for this is anassumed temperature of open- and closed-loop control unit 44 that isascertained by way of a characteristic curve 84. The time elapsed sinceinternal combustion engine 10 was started (block 86) is fed intocharacteristic curve 84. Characteristic curve 84 yields as its outputvalue the temperature of open- and closed-loop control unit 44 on theassumption of a certain starting temperature.

In 88, the difference is determined between the temperature ascertainedby characteristic curve 84 and a temperature ascertained and stored atthe last calibration, which is made available in block 90. In 92, aquery is made as to whether the difference ascertained in 88 is greaterthan a specific temperature difference, in the present case 10 K. If so,a calibration is performed and the temperature ascertained incharacteristic curve 84 is stored in memory 90.

As an alternative to this, however, a calibration action may bescheduled after expiration of a certain time interval. In order to takeinto account the asymptotic approach of the temperature of open- andclosed-loop control unit 44 to a terminal value, the length of the timeinterval after the internal combustion engine is started should beincreased in an appropriate manner.

The operation of an internal combustion engine with direct gasolineinjection has been explained in the exemplified embodiment above. It isunderstood, however, that the method described can also be used ininternal combustion engines that are operated with diesel fuel and areconfigured accordingly. Internal combustion engines that have an exhaustgas turbocharger and/or an exhaust gas recirculation system can also beoperated using the method described above.

1-14. (canceled)
 15. A method for operating an internal combustionengine in which fuel is injected directly into a combustion chamber byan injector that has a piezoactuator, the method comprising: determiningan electrical charge, which is at least one of conveyed to and removedfrom the piezoactuator, by a process that is calibrated at least onceduring an operating time span of the internal combustion engine; whereinthe process for determining the electrical charge at least one oftransferred to and removed from the piezoactuator is calibrated duringat least one triggering off-time of the piezoactuator while the internalcombustion engine is operating.
 16. The method of claim 15, wherein thecalibration is performed with the injector open, in the triggeringoff-time between an end of an opening triggering action and a beginningof a subsequent closing triggering action.
 17. The method of claim 16,wherein for each working cycle of a cylinder of the internal combustionengine, there is at least one secondary injection and one maininjection, and the calibration is performed during the main injection.18. The method of claim 16, further comprising: checking, before thecalibration, in a rotation-speed-synchronous dynamic interrupt, whethera time between two triggering actions is sufficient for the calibration.19. The method of claim 18, wherein an instruction necessary for thecalibration is determined in the rotation-speed-synchronous dynamicinterrupt.
 20. The method of claim 16, wherein the calibrationencompasses a plurality of individual calibration actions.
 21. Themethod of claim 20, wherein a number of actions possible per workingcycle of a cylinder is limited to a specific value, and only as manycalibration actions as will permit all intended injection actions to beperformed are allowed during one working cycle of the cylinder.
 22. Themethod of claim 15, wherein a calibration action is scheduled at leastwhen a temperature of a control unit has changed by at least a specificvalue since a last calibration action.
 23. The method of claim 15,wherein a calibration action is scheduled at least after expiration of aspecific time interval, a duration of the time interval increasing in adefined manner after a startup of the internal combustion engine. 24.The method of claim 15, wherein the calibration is performed during anoverrun condition of the internal combustion engine.
 25. A computerprogram executable on a computer, comprising: computer program code forperforming a method for operating an internal combustion engine in whichfuel is injected directly into a combustion chamber by an injector thathas a piezoactuator, the method including: determining an electricalcharge, which is at least one of conveyed to and removed from thepiezoactuator, by a process that is calibrated at least once during anoperating time span of the internal combustion engine; wherein theprocess for determining the electrical charge at least one oftransferred to and removed from the piezoactuator is calibrated duringat least one triggering off-time of the piezoactuator while the internalcombustion engine is operating.
 26. The computer program of claim 25,wherein it is stored at a memory or a flash memory.
 27. A control unitfor operating an internal combustion engine, comprising: a computerprogram executable on a computer of the control unit, including:computer program code for performing a method for operating an internalcombustion engine in which fuel is injected directly into a combustionchamber by an injector that has a piezoactuator, the method including:determining an electrical charge, which is at least one of conveyed toand removed from the piezoactuator, by a process that is calibrated atleast once during an operating time span of the internal combustionengine; wherein the process for determining the electrical charge atleast one of transferred to and removed from the piezoactuator iscalibrated during at least one triggering off-time of the piezoactuatorwhile the internal combustion engine is operating; wherein the computerprogram is stored at a memory of the control unit, and wherein thecontrol unit is one of an open-loop unit and a closed-loop unit.
 28. Aninternal combustion engine comprising: at least one combustion chamber;at least one injector to inject fuel directly into the combustionchamber; at least one piezoactuator; and a control unit for operating aninternal combustion engine, including: a computer program executable ona computer of the control unit, including: computer program code forperforming a method for operating an internal combustion engine in whichfuel is injected directly into a combustion chamber by an injector thathas a piezoactuator, the method including: determining an electricalcharge, which is at least one of conveyed to and removed from thepiezoactuator, by a process that is calibrated at least once during anoperating time span of the internal combustion engine; wherein theprocess for determining the electrical charge at least one oftransferred to and removed from the piezoactuator is calibrated duringat least one triggering off-time of the piezoactuator while the internalcombustion engine is operating; wherein the computer program is storedat a memory of the control unit, and wherein the control unit is one ofan open-loop unit and a closed-loop unit.